Merchant banker who set out to prove that a Montagu could still run the family business, and became chairman by the age of 41

THE 4th Lord Swaythling, who has died aged 69, was chairman of his family bank, Samuel Montagu & Co, and later of Rothmans International.

Lord Swaythling, known for most of his career as David Montagu, was a City aristocrat who was a rising star of the international financial scene in the 1970s, first at Samuel Montagu and subseqeuntly as head of Orion Bank, a Euro-market consortium venture.

He went on to be a director of several well-known companies, including The Telegraph plc, and in 1988 became chairman of Rothmans. The Rothmans group had interests in brands of luxury goods as well as in cigarettes, but in 1993 Swaythling presided over a restructuring which concentrated the company's activities in tobacco.

Although he came from a moneyed background, David Montagu rose on merit. As a financier, he was tenacious, imaginative and loyal to his clients; but he could also be outspoken, with an acerbic wit which did not endear him to everyone. When he adopted a cause, he fought very hard for it. The broadcaster John Freeman (whom Montagu helped to establish London Weekend Television) once described him as "someone I trust entirely, a man with whom I would go tiger shooting".

David Charles Samuel Montagu was born on August 6 1928, the eldest son of the third Lord Swaythling, a Liberal peer who served briefly as a partner of Samuel Montagu, but whose chief interests were in dairy farming and road safety; his most notable legislative achievement was to pilot the Bill which made rear lights obligatory on bicycles.

David's great-great grandfather, Louis Samuel, had moved from Liverpool to London in the early 19th century. Louis's son Montagu founded a banking partnership in 1853, and added Montagu to his surname in 1894 when he received a baronetcy. He sat as MP for Whitechapel, and was created Lord Swaythling in 1907. His second son, Edwin Montagu, became Secretary of State for India.

The family acquired substantial wealth and became part of the Edwardian haut juiverie. When the secret marriage of the third Lord Swaythling's youngest brother Ivor Montagu (a Communist film producer and founder-president of the International Table Tennis Federation) provoked a banner headline in the Evening News - BARON'S SON WEDS SECRETARY - Queen Mary wrote to the then Lady Swaythling: "Dear Gladys, I feel for you. May."

After his parents divorced in 1942, young David lived with his mother (a descendant of another branch of the Samuel dynasty, founders of the rival firm of Hill Samuel) and her second husband.

David was educated at Eton and Trinity College, Cambridge, where he switched from Law (he found it too dull) to English Literature. His Uncle Ivor (who had scraped a pass degree) had advised him that "there is only one reason for going to an English university, and that is to learn how to get drunk like a gentleman".

When David joined Samuel Montagu & Co, his father was the only family member in the partnership. Though the ownership had become diluted, David Montagu felt a duty to prove "that my family could still run a bank". The firm had a strong reputation in the acceptance market, as well as in foreign exchange, bullion dealing and corporate finance. Montagu became a director in 1954 and chairman in 1970, when he was only 41.

But by then one third of the trust which controlled the firm had been sold to Midland Bank. In 1973, when Midland bought the other two-thirds, Montagu was invited to become non-executive chairman. He thought himself far too young to accept such an impotent post: "A greater insult," he declared, "has never been offered."

Having resigned from Samuel Montagu & Co, he became chairman and chief executive of Orion Bank, a venture launched by a group of six international banks as a means of entry into the rapidly developing Eurobond and syndicated loan markets.

He improved Orion's performance and greatly enlarged its reputation. But the consortium arrangements proved unwieldly, and Montagu eventually told his shareholders that it was "a very expensive form of dining club" which they would do better to sell to a single owner.

The shareholders spurned his advice, and Montagu left Orion in 1979. Within 18 months one shareholder, Royal Bank of Canada, bought out all the others.

After a brief, unhappy spell with the American brokerage firm Merrill Lynch, Montagu found a more congenial berth as deputy chairman of J Rothschild Holdings, the private investment house of his old friend Jacob (now Lord) Rothschild. He was also a non-executive director of LWT, and of the construction group Bovis.

In 1985, he was invited by Lord Hartwell to join the board of The Daily Telegraph. He stayed on until 1996, a valued supporter of the subsequent proprietor Conrad Black.

Montagu also served on the investment committee of the United Nations, and on the Bank of England committee of inquiry into the collapse of Barings.

Having succeeded to the peerage on the death of his father in 1990, he delivered a maiden speech in the Lords in favour of the War Crimes Bill - but rarely attended the House in later years.

A man of fastidious, civilised tastes who once called himself "a lobster-eating Jew", David Montagu was an art collector, a theatre lover, a connoisseur of fine wine and cigars and a keen bridge player.

He also kept a string of racehorses near his Newmarket home. Perhaps his best-known horse was Zongalero, who finished second to Rubstic in the 1979 Grand National. He was a founder member of the British Horseracing Board, chairman of its finance committee, and a member of the All-Party Racing and Bloodstock Committee.

He was president of the Association for Jewish Youth.

He married, in 1951, Ninette Dreyfus, daughter of Edgar Dreyfus, of Paris. They a son and two daughters (one of whom died in 1982). The son, Charles Edgar Samuel Montagu, born in 1954, is heir to the peerage and the baronetcy.